The present invention relates to. a method and apparatus for measuring the growth of biological material and the deposition of organic and inorganic contaminants on coupons, and for screening agents useful for regulating the growth of biological material and the deposition of organic and inorganic contaminants. More particularly, the present invention is directed to a method and apparatus for measuring the growth of biological material and the deposition of organic and inorganic contaminants on coupons.
Many industrial processes, such as pulp and paper making, utilize water and/or other liquid material in processing steps. Such process liquid typically provides an excellent supply of carbon and nutrients which promote bacterial growth. In paper mills, for instance, bacterial films (xe2x80x9cbiofilmsxe2x80x9d) undesirably and readily forms on the steel surfaces of process equipment used during manufacture. Such biofilms typically are accompanied by protective exopolysaccharides (xe2x80x9cslimexe2x80x9d) and occur at the interface of these equipment surfaces and process water streams. Additionally, inorganic contaminants, such as calcium carbonate (xe2x80x9cscalexe2x80x9d) and organic contaminants often deposit on such surfaces. These organic contaminants are typically known as pitch (e.g., resins from wood) and stickies (e.g., glues, adhesives, tape, and wax particles).
The growth of biofilm and the deposition of these inorganic and organic contaminants can be detrimental to the efficiency of such equipment causing both reduced product quality, reduced operating efficiency, and general operational difficulties in the systems. Deposition of organic contaminants on consistency regulators and other instrument probes can render these components useless, and deposits on screens can reduce throughput and upset operation of the system. This deposition can occur not only on metal surfaces in the system, but also on plastic and synthetic surfaces such as machine wires, felts, foils, Uhle boxes and headbox components. The difficulties posed by these deposits include direct interference with the efficiency of the contaminated surface, resulting in reduced production, as well as holes, dirt, and other sheet defects that reduce the quality and usefulness of the paper for operations that follow like coating, converting or printing.
Consequently, methods of preventing and removing the build-up of such deposits on pulp and paper mill equipment surfaces are of great industrial importance. While paper machines can be shut down for cleaning, this is undesirable as it necessarily results in a loss of productivity of the machine. Additionally, the product produced prior to such cleaning is often of poor quality due to contamination from deposits which break off and become incorporated into product sheets. Likewise, removing such deposits also necessarily results in the formation of poor quality product which is manufactured prior to such deposition removal. Preventing deposition of such contaminants is thus greatly preferred as it allows for consistently high quality product to be produced in an efficient manner.
Additionally, the deposition of slime and other contaminants on metal surfaces promotes both corrosion of such surfaces and fouling or plugging of pulp and paper mill systems. Typically, the deposits become entrained in the paper produced and cause breakouts on the paper machines with consequent work stoppages and the loss of production time. These deposits also causes unsightly blemishes in the final product, resulting in rejects and wasted output.
These contamination problems have resulted in the extensive utilization of contamination control agents, such as biocides, in water used in pulp and paper mill systems. Agents which have enjoyed widespread use in such applications include chlorine, organo-mercurials, chlorinated phenols, organo-bromines, and various organosulfur compounds, all of which are generally useful as biocides but each of which is attended by a variety of impediments. Particularly, the use of compositions comprising polyvinyl alcohol and gelatin, such as those described in U.S. Pat. No. 5,536,363 to Nguyen, have been found to be well suited for regulating the deposition of organic contaminants in pulp and papermaking systems. Further, conditions such as temperature, pH, and the presence of organic and inorganic materials vary greatly among and within manufacturing processes, resulting in a need for agents which serve to destroy and regulate the growth of such materials that form on process equipment functioning under these various conditions.
It is known to monitor the presence of biofilm and other contaminant materials in process water streams, such as through the methods and apparatuses described in U.S. Pat. No. 2,090,077 to Thorne, U.S. Pat. No. 5,049,492 to Sauer et al., U.S. Pat. No. 5,155,555 and 5,264,917 both to Wetegrove et al., U.S. Pat. No. 6,017,459 to Zeiher et al., and U.S. Pat. No. 6,053,032 to Kraus et al. which allow for the sampling of water during manufacturing processes.
As illustrated by these references, known methods and apparatuses for determining the presence of contaminants in process water streams include contacting a substrate, known in the art as a coupon, with a process water stream for a period of time, removing the substrate from the stream, and then subjecting the coupon to analysis. Such analysis typically involves staining and microscopy, visual inspection, or light transmission. Each of these methods and apparatuses, however, has drawbacks such as requiring that the coupon be removed from the fluent sample and attended to by a person for analysis. Further, the qualitative nature of certain methods, such as staining and microscopy, make it difficult to reproduce results obtained thereby when such methods are part of an experimental design.
Accordingly, there exists a need for a method and apparatus which allows for the continuous and automatic quantitative measuring of the deposition of biofilm and other contaminants on a coupon in process water streams and which allow for the investigation of agents useful for regulating contaminant deposition.
In a method aspect of the present invention, the present invention provides a method for measuring the deposition of organic and inorganic contaminants on a coupon. The method includes the steps of: (i) supporting a coupon in a fluid sample; (ii) separating the coupon from the fluid sample; and (iii) weighing the coupon. The weight of the coupon increases where contaminants present in the fluid sample deposit on the coupon.
The present invention may also include the step of permitting the coupon to dry for a predetermined period of time prior to weighing and may include the step of measuring the weight of the coupon prior to supporting the coupon in the fluid sample. Successive weight measurements may be taken at predetermined intervals and the difference between these successive weight measurements may be recorded. Further, the coupon may be separated from the fluid sample, which may be provided as a current across the coupon, by draining the fluid sample-from the coupon. Contaminant control agents, such as biocides, may also be added manually or automatically to the source of the fluid sample to control the presence of contaminants, such as biofilm, in the source.
In another aspect of the present invention is provided an apparatus for measuring the deposition of contaminants, such as biofilms, on a coupon. The apparatus includes a reservoir tank defining a reservoir cavity for receiving a coupon, a fluid inlet means in fluid communication with the reservoir cavity, a fluid outlet means in fluid communication with the reservoir cavity, a coupon suspension member adapted for supporting a coupon within the reservoir cavity, and a weight sensor coupled to the coupon suspension member. The fluid sample contacts a coupon supported by the coupon suspension member.
The apparatus may further include a substantially elongate planar coupon supported by the coupon suspension means and may include a computer system associated with the weight sensor means which is capable of computing data received from the weight sensor so as to determine the weight of the coupon and any contaminant deposition thereon. The reservoir tank may include a valve for draining the fluid sample from the reservoir cavity.
Further, the apparatus may include a first fluid circuit line in fluid communication with the reservoir tank, where the first fluid circuit line permits the fluid sample to enter the reservoir tank. Additionally, the apparatus may include a second fluid circuit line in fluid communication with the reservoir tank, where the second fluid circuit line permits the fluid sample to exit the reservoir tank. A pump may also be included for drawing the fluid sample from a fluid source to the reservoir tank.